1. Field of Invention
The invention relates generally to the field of intrusion detection systems for animate, inanimate or gaseous substances relying on infrared signal detection and, more specifically, to a space safety infrared signal intrusion detection system which incorporates a micro-electro-mechanical system (MEMS) mirror array.
2. Description of Related Art
Passive infrared (IR) sensors detect intruders moving within the field of view (FOV) by measuring the temperature gradient caused by an intruder. The sensor's FOV is fixed and is determined by the optical properties of the lens or mirror system. The FOV is subdivided into static active and inactive zones; the motion of an intruder from an active to an inactive zone is detected as an alarm. The IR energy from each active zone is focused on the IR detector and the IR detector cannot determine which active zone is collecting the energy. The problem with this arrangement is that other sources of IR energy within a zone or zones can be detected as alarm signals as well. Examples include a space heater cycled on and off or a sunlit shade moving from a breeze within the detector's zones. Other sources of noise include a pet such as a small dog. Also, the inactive zones offer a path that an intruder can traverse without detection. Others have tried to solve these problems as follows: One product has an algorithm to detect repetitive motion within a zone and desensitize the detector to ignore this signal. This also desensitizes the sensor to intruders as well. Another approach uses a CCD camera to monitor the protected space and employs video processing algorithms to detect motion. The problem with this approach is that the protected space needs to be illuminated to detect the motion. Another approach uses a second lens system to minimize the inactive zones but this approach still suffers from the other shortcomings.